The present invention relates to an apparatus for analyzing particulate matter or materials suspended in the atmosphere.
In the particulates suspended in air or atmosphere, those having aerodynamic particle diameters below 10 μm are referred to as suspended particulate materials (SPM). Although soil entrained in air is also included, suspended particulate materials are composed predominantly of diesel smoke, incompletely burned fuel, and sulfur compounds (35% originate from diesel powered vehicles in the Kanto region in Japan), and is highly harmful. The particulate materials attributable to diesel emissions are referred to particularly as DPE. Particulate materials with an aerodynamic diameter below 2.5 μm are referred to as micro-particulate materials (PM2.5), which have been investigated or researched vigorously in the United States and Europe. In the case of PM2.5, the percentage of diesel powered vehicles as emission sources is believed to be even higher.
As an apparatus for collecting such particulate materials suspended in the atmosphere, one that utilizes an impactor is well known. The apparatus with an impactor collects particles by separating them from a flowing mass that is collided with a collecting plate, thereby rapidly changing the direction of the air flow. Since such an apparatus utilizing the impactor cannot collect particles in the submicron- to nano-particle range, the present inventor has proposed a method in which air is introduced into a container, a discharging electrode to generate mono-polar ions and a dust collecting electrode having an electric potential difference relative to the discharging electrode are arranged in the container, the particulate materials contained in the air introduced into the container is electrically charged by mono-polar ions, and the charged particulate materials are collected on the dust collecting electrode and made available for various measurements and analyses (see, for example, patent reference 1).
The present inventor, moreover, has also proposed an apparatus including a differential mobility analyzer (DMA) disposed at an air inlet of the above described container having the discharging and collecting electrodes disposed therein. The differential mobility analyzer utilizes differences in mobility of particles based on their particle size, and, by using an electric field, allows only the particulate materials falling within a selected particle size range to pass. Thus, only the particulate materials falling within the selected particle size range are collected on a collecting electrode (see patent reference 2).
Patent Reference 1: Japanese Patent Laid-out Publication No. 2003-215021
Patent Reference 2: Japanese Patent Laid-out Publication No. 2003-337087
In case of analyzing the components, particularly volatile components, of particulate materials suspended in the atmosphere, an analysis using an analyzer, such as a gas chromatograph, for example, must be carried out on the particulate materials collected. In the case wherein a conventional apparatus having an impactor is used to collect particulate materials, the aforementioned submicron- to nano-particle range particulate materials can not be collected. Moreover, as the apparatus is incapable of collecting particulate materials under atmospheric pressure (collects under reduced pressure), the volatile components of particles can be lost. The apparatuses disclosed in patent references 1 and 2, on the other hand, can collect submicron- to nano-particle range particulate materials, and do not lose volatile components since the collection is carried out under atmospheric pressure.
In cases wherein particulate materials are collected by using the apparatuses disclosed in patent references 1 and 2, however, the dust collecting electrode must be removed by opening the container after collecting particulate materials on the dust collecting electrode over a certain period of time for an analysis using an analyzer. This can be extremely labor intensive, and thus impractical, when conducting a time-series analysis that focuses on changes in the components of particulate materials over a prolonged period of time.
The present invention has been proposed in view of such situations, and it is an object of the invention to provide an apparatus for analyzing suspended particulate materials capable of accommodating time-series analyses of the volatile components of particulate materials suspended in the atmosphere.
It is another object of the present invention to provide an apparatus for analyzing particulate materials suspended in the atmosphere capable of analyzing the volatile components of particulate materials according to particle size.